In a semiconductor device manufacturing process for forming a lamination structure of an integrated circuit on a surface of, for example, a semiconductor wafer (hereinafter, referred to as a “wafer”) that is a substrate, there is a liquid processing process for processing a surface of the wafer using a liquid, such as, for example, removing fine dust or a natural oxide film from the surface of the wafer by a cleaning liquid such as, for example, a chemical liquid.
According to high integration of semiconductor devices, however, a phenomenon, so-called a pattern collapse, becomes a problem when removing, for example, liquid attached to a surface of a wafer in such a liquid processing process.
The pattern collapse refers to a phenomenon in which, when liquid remaining on a surface of a wafer is dried, the liquid remaining in an uneven area forming a pattern, for example, the liquid remaining on the left and right of a convex portion (in other words, in concave portions) is unevenly dried so that the balance of surface tension that draws the convex portion to the left and right is lost and thus the convex portion falls over to the direction where more liquid remains.
As a method of removing liquid attached to a surface of a wafer while suppressing the occurrence of such a pattern collapse, a method of using a supercritical high-pressure fluid is known. The supercritical high-pressure fluid has a low viscosity compared to a liquid, and also has a high performance of extracting the liquid. Further, no interface exists between the supercritical high-pressure fluid and a liquid or gas in an equilibrium state. Thus, when the liquid attached to the surface of the wafer is substituted with the supercritical high-pressure fluid and then the supercritical high-pressure fluid is changed into a gas state, the liquid may be dried without being affected by the surface tension.
For example, in Japanese Patent Laid-Open Publication No. 2011-187570, hydrofluoro ether (HFE)—a fluorine-containing organic solvent (in the Japanese Publication, referred to as a “fluorine compound”)—is used for both of a dry preventing liquid and a supercritical high-pressure fluid from the point of view of a substitutability level between the liquid and the supercritical high-pressure fluid or suppression of carry-in of moisture at the time of liquid processing. In addition, the fluorine-containing organic solvent is also suitable for the dry preventing liquid in view of the fact that it is fire-resistant.
However, when the liquid on the surface of the wafer is dried using the supercritical fluid as described above, it is difficult to remove the liquid without causing pattern collapse so that the pattern collapse phenomenon is left in the wafer.